Parts of the background of the invention are set out in U.S. Pat. Nos. 3,668,103 and 3,767,504 and to the extent necessary for an understanding of this invention, the two patents are incorporated herein by reference.
Using a metal strip embedded in a plastic body to reinforce the body against bending and twisting is described broadly in both the above cited patents. The metal strip is oriented such that it will best minimize bending in one particular direction and certainly minimize all bending to some extent. The fluid tight plastic enclosure is usually necessary to protect the metal strip from the corrosive atmosphere is which the apparatus operates.
The prior art provides for a metal strip having a thickness T, a width W, and a length L. A groove is cut in the plastic body to house the metal strip with the thickness of the groove being slightly greater than T, the depth being slightly greater than W, and the length being slightly greater than L. It is desired to have as little play as possible between the sides of the groove and the strip because the reinforcing against bending is active only when the force is acting on the metal strip. A strip of plastic is laid over the metal strip and then a weld bead of compatible plastic is laid over the plastic strip, thereby melting both sides of the groove and a part of the plastic strip to bond all three together in a melting and solidifying sequence. This invention has improved on both the method of reinforcing the plastic bar as well as improving the stability of the hanger bracket.
For convenience, a brief description will be made of the hanger bracket although, as explained subsequently, the method itself used in the hanger bracket construction is broadly applicable in other structural embodiments including those similarly involved in fluid treatment barrels such as are used in electroplating, phosphating, or the like.
The prime problem with the prior art is maintaining the fluid tight envelope around the metal bar and if a break occurs, it occurs when the plastic weld material contacts the metal bar directly during the welding process and thereby bonds to it. The particular welding mechanism described in the two above cited patents is somewhat more delicate than the designs submitted herewith which are substantially less complex in terms of the ease of assembly and degree of skill necessary in the assembly. Instead of the two step sequence provided before of laying a plastic strip of width T over the metal strip and then welding over the plastic strip, in this instance a plastic rod much greater in width than T is welded flush with one face of the plastic bar to be strengthened or reinforced. A groove is previously cut in the bar, the rod, or both, of a size to accommodate the metal strip which is oriented in the desired direction.
Stated differently, the groove may be cut completely in the bar to be strengthened, in the rod to be welded to the bar or partially in each so long as the result is a groove of a size to accommodate the metal strip in free floating condition with minimum play. A plastic bead is then laid completely around the edge of the rod where it is juxtaposed to the bar to weld the bar and rod together as a unit. In this manner the plastic weld completely seals the metal strip in fluid tight confinement within the bar-rod envelope and there is no danger of the plastic melt bonding to the bar itself because of the distance of the plastic weld from the strip.
Where small problems existed in the past with melt adhereing to the metal strip, the integrity of the plastic envelope would sometimes be impaired by a tearing of the delicate membrane over the metal strip upon sequential heating and cooling due to the differential in coefficient of thermal expansion between the plastic and the metal. As a general rule, polypropylene or the like is the plastic material comprising the rod and bar as well as the weld material; and as is well known, polypropylene has a higher coefficient of thermal expansion than the preferred steel strip. As a consequence, the obvious would occur and where the plastic had bonded to the steel at spaced apart locations the plastic would either break loose from the steel on the first heating or cooling or else it would tear the plastic weld bead and allow corrosive fluids to pass through the break and corrode the metal strip.
The improvement here removes the plastic weld to more remote positions relative to the metal strip and thus eliminates any possibility of a plastic bond to the metal strip.
In conventional electroplating activities the electroplating fluid in the tanks is sometimes heated to 195.degree.F. As a result the barrels which are dipped into the electrolyte are heated from ambient temperatures to roughly 195.degree.F. The result is a thermal expansion of the barrel in length of up to 1/4 inch on some occassions (on a 36 inches long barrel). Considering this situation and the fact that there are two hanger brackets, one at each end of the barrel, manufacturers in the past have traditionally done one of two things to compensate for this expansion:
a. Arrange the hanger brackets on the barrel support frame such that they are spaced apart a distance of up to 1/8 inch greater than is necessary to firmly support the barrel at ambient temperatures. Obviously, this arrangement allows the barrel to slop back and forth on the hubs until it is heated to the extent that the hubs of the barrel are in proper abutting arrangement with the hanger brackets. The result is clear, (1) excess wear due to a sloppy fit, (2) excess bending of the hanger brackets as the loaded barrel oscillates back and forth and differential wear on the gear teeth of the idler gear and the barrel gear. PA1 b. The hanger brackets are initially arranged a distance apart such that there is a relatively tight fit of the barrel between the hanger bracket at ambient temperatures in which case, when the barrel is immersed in the hot electrolyte it expands the length of the barrel. This deflects the hanger brackets and slightly misaligns the teeth of the drive gear mounted on the drive shaft, the idler gear mounted on the hanger bracket, and the driven barrel gear mounted on the hub of the barrel. The obvious problem here is that the teeth of the gears involved will become more worn in some places than in others and in addition the bending moment resulting from the drive gear will be multiplied by a lengthening lever arm the more the hanger bracket bends. Additionally the bending can cause some binding between the hub and the circumferential bearing around the hub.
In this invention the hanger brackets are first constructed in the novel manner herein disclosed with the metal bar embedded in free floating condition within the bracket, in fluid tight confinement and then the hanger bracket is given a prestressed camber or deflection inward toward the barrel. Obviously, it is the metal strip which is deformed rather than the polypropylene which has much greater flexibility. Subsequently, the idler gear is mounted in proper position with consideration of the slight deflection.
Angle irons are conventionally used to join the bracket to the barrel support frame. A pair are welded to opposite edges of a U-shaped channel which serves as a lift bar for the frame. The downwardly extending pair of angle irons are bolted to upwardly extending legs of the bracket. This invention provides an improvement over the prior art by using longer angle irons which extend about halfway down the bracket. The longer angle irons minimize deflection of the bracket beyond the straight line point and thereby minimize misalignment of gear teeth.
Some barrels used in conventional apparatus are not gear driven. Rather, they are driven by V-belts. Some belt driven barrels use rather long hanger brackets and only by using the novel sealed, metal strip reinforced hanger brackets as herein disclosed can gear driven barrels be substituted for V-belt driven barrels. Twisting and bending hanger brackets are not so severe a problem with flexible and resilient V-belts as similar twisting and bending would be with a gear drive. To substitute gears for belts the bracket must have proper rigidity to ensure proper teeth engagement. With particularly long hanger brackets, a plurality of idler gears may be mounted on the hanger bracket and it is clear that the longer the bracket, the more rigid must it be to maintain proper gear teeth engagement. It is an object of this invention to provide a suitably rigid hanger bracket for a plurality of idler gears and even to support the drive shaft. It has been demonstrated experimentally that virtually any fluid is a lubricant for plastic. Consequently, when the apparatus disclosed is operated according to design instructions the electrolyte in the treatment tank serves to lubricate the support axle of an idler gear where it rotates in the cylindrical bearing in the hanger bracket. Unfortunately, some persons do not operate the equipment as it was designed to operate. Conventionally, the idler gear is partially immersed when the barrel rotates. Occasionally, the level of electrolyte is not maintained or the barrel is not fully immersed. Thus, the idler gear bearing gets no lubrication. Normally the bearing operates at just over 200.degree.F. However, without the electrolyte lubrication, normal barrel rotation causes the dry bearing to heat above 450.degree.F. within ten minutes and the idler gear shaft melts. To protect against inadvertant improper operation the improved hanger bracket of this invention provides a self contained lubricant reservoir and passage means to the bearing-idler gear shaft interface.
A brief description of the drawings follows along with a more detailed description of the preferred embodiment which will more completely explain the novel concepts and structures involved.